They were content with being slaves and raped by their own people in africa but when white people came they also took them to a foreign land. That's the only logical reason why they would be mad. Instead of being raped in their own lands it was somewhere else.

before the African slave trade, slavery as a form of punishment wasn't common. there were a few crimes which would warrant enslavement but the majority were just killed of maimed as punishment. It wasn't until Europeans showed up looking to purchase slaves for the plantations in the America's that slavery became a common punishment for criminals in African kingdoms, it also spurred wars for the purpose of generating more slaves to trade for weapons. It was also a common belief that the White Europeans were purchasing so many Africans because they thought Whites were cannibals and were eating the slaves.